This should be a powerful piece of work and it is for sure. But it has the feel of being stage managed (I am sure it wasn't) which sort of works against it, for my anyway.
I don't know the answer but I think perhaps the couple form an almost seperate image to that of the unfortunate homeless guy. A couple of steps more to close the gap and bingo - problem solved or you could have moved you position to the left - maybe
I think also I would lose some of the fg pavement.
On a completely different tack - why not give the homless guy a go with the camera - so he can take a picture of the people walking by - now you have me thinking.